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Antibody enzyme immunoassay improves rapid detection of Histoplasma
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Antibody detection by enzyme immunoassay could reduce the number of acute pulmonary histoplasmosis cases missed by other widely used rapid diagnostics, according to recent data.
The test, which allows for separate detection of immunoglobulin G (IgG) and immunoglobulin M (IgM), also could be combined with established antigen detection tools for an increased sensitivity of more than 95%, the researchers wrote.
“Once suspected, the diagnosis of acute pulmonary histoplasmosis can usually be established promptly by detection of antigen in the urine or serum,” they wrote. “In one study, antigen was present in 83% of acute pulmonary histoplasmosis cases but 38% would have been missed if only urine was tested. An antibody assay could assist in the diagnosis of cases with negative antigen results, especially those with mild to moderate disease.”
To examine the sensitivity of the MVista (MiraVista Diagnostics) Histoplasma antibody enzyme immunoassay (EIA), researchers collected serum specimens from patients previously identified with histoplasmosis, as well as from controls with no history of histoplasmosis. Anti-Histoplasma antibody standards were prepared with these samples, along with dilutions of these pools to obtain standard curves for IgG or IgM testing. Sensitivity and specificity of EIA was analyzed independently for IgG and IgM, with results compared with those of immunodiffusion (ID), complement fixation (CF) and antigen detection strategies collected from CDC or other sources.
At the optimal cutoffs, the researchers determined the EIA’s IgG detection sensitivity (87.5%) and specificity (95%), while IgM detection sensitivity was 67.5%; the specificity was 97%. Combining these antibody results led to a sensitivity of 88.8% and a specificity of 91.9%. The test’s overall sensitivity was greater than that demonstrated by ID (55%), CF (73.1%) and antigen testing (67.5%).
These results were highly reproducible, the researchers wrote, and the platform’s capacity to report both IgG and IgM antibodies could be useful when distinguishing between current and past infection. In addition, the 96.3% sensitivity achieved by combining antigen and antibody provides a strong case for performed both tests when diagnosing patients.
“The MVista antibody EIA has the potential to complement antigen detection in the diagnosis of acute pulmonary histoplasmosis, identifying cases that are falsely negative by ID and/or CF, and helping to differentiate histoplasmosis from related mycoses,” the researchers wrote. “A combination of antibody and antigen testing may provide the highest diagnostic yield for acute pulmonary histoplasmosis.” – by Dave Muoio
Disclosure: Richer reports being an employee of MiraVista Diagnostics. Please see the full study for a list of all other researchers’ relevant financial disclosures.
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